Bidirectional video telephony between cable television and switched telephone systems

ABSTRACT

In a video telephony system, a coaxial cable network, which is preferably a part of an existing cable television system, provides a local link for the transmission of the video telephone signals between each originating and destination location and a respective &#34;head end&#34; located on the cable company premises. Each of the head ends is connected to a &#34;point of presence&#34; of a telephone interexchange carrier so that a connection between pairs of head ends, and thus between a pair of video telephone locations, can be made via a switched digital network maintained by the carrier. Certain of originating and destination locations comprise a standard television set, serving as the audio/video display, and a consumer-type camera or camcorder, serving as the audio/video source. Others of the originating and destination locations comprise ISDN video telephones which are connected to the various points of presence of the interexchange carrier via local exchange carrier telephone networks. The video telephone number for cable subscriber locations are administered to be the same as the standard ten-(i.e., area code plus seven-) digit telephone number used for regular telephone calls directed to those locations.

FIELD OF THE INVENTION

This invention relates generally to video telephony and, morespecifically, to bidirectional transmission of voice and pictureinformation among a large number of geographically distributed users.

BACKGROUND OF THE INVENTION

Because two-way video communications can give individuals the ability tocommunicate graphical information and to see facial expressions andgestures that cannot be conveyed by audio alone, much emphasis has beenplaced on commercial development of such systems. Indeed, videotelephones that work with analog telephone lines have been demonstrated.However, due to the limited bandwidth of conventional telephone lines,and the consequent limitation on the amount of information that can becarried therethrough, commercial development has been limited toless-than-full-motion video presented on a small display.

In order to overcome the bandwidth limitation associated with videotelephony transmitted over the analog telephone lines, video telephonesmore recently have been designed to work with digital telephone accesslines, such as ISDN. However, at the present time, digital accessfacilities to consumer homes are not readily available.

Other systems use optical fiber directly linked to subscriber homes inorder to obtain the high bandwidth needed for full motion video.However, these facilities are expensive, and thus are not accessible tothe ordinary household. Besides, it will be decades before most homesare provided with fiber access.

The above-outlined problems are substantially ameliorated by thearrangement disclosed in the co-pending, commonly assigned United Statespatent application of C. D. Yu entitled "Bidirectional Video TelephonyUsing Shared Channels on Coaxial Cable Networks," Ser. No. 787,436,filed Nov. 4, 1991. In a disclosed embodiment of the Yu arrangement, theterminal equipment comprises a standard television set, serving as theaudio/video display, and a consumer-type camera or camcorder, serving asthe audio/video source. A coaxial cable network, which is preferably apart of an existing cable television system, provides a local accesslink for the transmission of the video telephone signals between eachoriginating and destination cable subscriber location and a respective"head end" located on the cable company premises. A network interfaceunit, or NIU, at each location provides a control interface between theterminal equipment and the cable television distribution network to dealwith such "housekeeping" chores as allocation of upstream and downstreamvideo telephone channels between the subscriber location and the headend, receiving of "dialing" information from the subscriber, etc. Eachof the head ends is connected to a "point of presence" of a telephonecommon carrier-illustratively an interexchange carrier such as AT&T-sothat a connection between pairs of head ends, and thus between a pair ofvideo telephone locations, can be made via a switched network maintainedby the carrier.

SUMMARY OF THE INVENTION

In accordance with the present invention, the usefulness of a videotelephony system which uses cable television distribution networks toconnect cable subscriber locations to the telephone network is enhancedby providing the system with the capability of allowing cable subscriberlocations to communicate with non-cable subscriber locations, such aslocations that are connected to the switched digital network exclusivelyvia telephone facilities (including locations reached via dialing 800 or900 numbers of international destinations). The invention thus enablesparties who possess a video telephone, but are not served by avideo-telephony-capable cable television distribution network, tocommunicate with parties who are so served but who do not possess avideo telephone. Advantageously, the telephone facilities may include anISDN connection which supports communications between the point ofpresence and an ISDN video telephone. However, the inventioncontemplates that other types of connections--to which are connectedother types of video telephony equipment--may be used including, forexample, non-ISDN video telephones which communicate over standard voicechannels.

In preferred embodiments, a database containing information about cablesubscriber locations is maintained and made available to the switcheddigital network. When a request to establish a video telephoneconnection over the switched digital network is received at theoriginating point of presence, the database is accessed to determinewhether the selected destination location is or is not a cablesubscriber location. Note that, in accordance with the invention, thatconnection request received at the originating point of presence mayhave originated either from a cable TV head end or via telephonefacilities exclusively. If the selected destination location is, infact, a cable subscriber location, the connection is established to thecable television distribution network head end and thence down to thedestination location itself. If not, the call is routed via conventionaltelephone facilities.

The database may also contain information about non-cable subscriberlocations, such as the data rate at which video telephone equipment atthose locations operate, thereby allowing the system to extend videotelephone signals to such locations at an optimum data rate. If thedatabase does not contain information about a particular cablesubscriber location, the equipment thereat is assumed to operate at apredetermined, default rate.

BRIEF DESCRIPTION OF THE DRAWING

Further aspects and features of the invention will become apparent froma consideration of the following detailed description and accompanyingdrawing, in which

FIG. 1 is a block diagram illustrating a video telephony systemembodying the principles of the invention;

FIG. 2 is a block diagram of an analog network interface unit that canbe used in the system of FIG. 1;

FIG. 3 is a block diagram of a cable head end used in the system of FIG.1;

FIG. 4 is a block diagram of a video enhanced services platform (VESP)used in the system of FIG. 1;

FIG. 5 is a block diagram of point of presence (POP) equipment used inthe system of FIG. 1;

FIG. 6 is a block diagram of a digital network interface unit that canbe used in the system of FIG. 1 instead of the analog network interfaceunit of FIG. 2;

FIG. 7 shows the inter-relationship between FIG. 3 and FIG. 4;

FIG. 8 is a flowchart setting forth the logical sequence of stepsimplemented within the system of FIG. 1 to achieve connections betweendifferent types of subscriber locations which are served by the system;

FIG. 9 depicts a portion of a database maintained within a video networkcontrol point (NCP) that is within the system of FIG. 1; and

FIG. 10 is an enlarged view of one of the subscriber locations in thesystem of FIG. 1.

DETAILED DESCRIPTION

The block diagram of FIG. 1 shows a video telephony system similar tothat disclosed in the above-cited Yu patent application. In particular,an originating cable subscriber location 101 is shown to be able tocommunicate to a selected destination cable subscriber location 105 in avideo telephone call established via a switched digitaltelecommunications network 160, the latter being part of aninterexchange carrier (IXC) network 150. Cable subscriber locations 101and 105 are illustratively private residences, although they need notbe. The gateways to network 160 are point of presence (POP) locations161, 162, which are described in more detail below.

Originating and destination cable subscriber locations 101 and 105 areconnected to POPs 161 and 162, respectively, via connections whichinclude respective connections through cable television distributionnetworks 121 and 126. In particular, audio and video communicationbetween a network interface unit (NIU) 104 (described in more detail inconnection with FIGS. 2 and 6) positioned within originating cablesubscriber location 101 and originating head end 122 (located on cablecompany premises) uses coaxial cable television distribution network121, which includes a series of bidirectional (i.e., forward and reversedirection) amplifiers. Such amplifiers are currently available in threebandwidth split categories from sources such as Scientific Atlanta,Jerrold and Magnavox. Within head end 122, cable head end 124 filtersand separates the received signal so that only the portion of RFbandwidth that is dedicated to video telephony is demodulated andapplied to a video enhanced services platform, or VESP, 125 withinoriginating head end 122. The portion of the RF bandwidth that is usedfor "entertainment channels" received from downstream entertainmentchannel source 130 is modulated by existing head end equipment andapplied to existing cable system facilities that form no part of thepresent invention. Cable head end 124 and VESP 125 can be physicallylocated at the same or different locations.

Other cable subscriber locations (not shown) have similar associatedconnections to head end 122 via coaxial cable television distributionnetwork 121 in a tributary type structure and receive the same signalsthat are in effect "broadcast" on coaxial network 121.

Typically, the RF spectrum between 5 MHz and 30 MHz on cable network 121is reserved for upstream use. Accordingly, four 6 MHz channels cansimultaneously carry upstream analog audio and video signals in NTSCformat. However, the coaxial bandwidth can be split in other ways forupstream and downstream use, so that a different number of upstreamchannels may be available for either upstream video telephone signals orentertainment signals. For example, digital video compression technologyhas made possible packing several (e.g., 4) video signals in one 6 MHzbandwidth. Throughout this specification, analog video telephonechannels will be assumed to have a 6 MHz or less bandwidth. The capacityof digital channels will be denoted in terms of kilo bits per second.

In VESP 125, the demodulated audio and video signals are converted to acompressed digital signal, multiplexed with other digital signals, andsent to POP 161 as a 384 Kb/s composite signal via a digitalcommunications channel 131, using an ISDN primary rate interface (PRI)connection along with other so-called DS1 transmission facilities whichare controlled by the D channel of the PRI connection using standardnon-facility-associated signaling. (In the drawing, an ISDN connectionis shown as a pair of lines-a solid line representing the B channels anda dotted line representing the D channel.) The composite digital signalis then demultiplexed and one digital signal is transported from POP 161to POP 162 via the digital switched telephone network, which may beAT&T's switched 384 Kb/s network.

After the end-to-end link between the originating and destination headends is established, the digital audio/video signal is transmitted todestination POP 162. The digital signal received in POP 162 ismultiplexed with other digital signals destined for the same destinationcable network and the composite signal is transmitted to destinationhead end 127 via a digital communication channel 136 using an ISDN PRIconnection. In a similar fashion to that just described, audio and videocommunication between head end 127 and destination location 105 uses thecoaxial cable distribution network 126 serving destination location 105,which connects the cable head end 128 within destination head end 127 toa network interface unit 108 positioned within destination location 105.VESP 129 transforms digital signals back to analog audio and videosignals, which are then modulated to specific RF carriers allocated forvideo telephony. Other locations (not shown) are tied into coaxial cabledistribution network 126 in a tributary type structure, so that signalson cable distribution network 126 can represent video telephoneinformation concurrently originating in or destined for severallocations, as well as "entertainment channel" information provided bydownstream entertainment channel source 135 and combined in cable headend 128. As with originating head end 122, the cable head end 128 andVESP 129 within destination head end 127 can be physically located atthe same or different locations.

Before proceeding further, it may be observed at this point that,although the establishment of a connection between the originating anddestination cable subscriber locations has been described as proceedingstep-by-step from the former to the latter, other techniques forestablishing the end-to-end connection may be used. One possibility isto proceed step-by-step in the opposite direction. Another is toestablish connectivity from the destination location up to itsassociated VESP and then proceeding step-by-step from the originatingsubscriber location to that VESP.

Within originating cable subscriber location 101 and destination cablesubscriber location 105, audio and video signals are originated bycameras 102 and 107, respectively, and received and displayed onconventional television sets 103 and 106, respectively. These elementsare connected to and interact with NIU 104 and 108, respectively, in amanner to be explained more fully below. It will be understood that anyaudio/video origination source (such as a camcorder or video tapeplayer) can be used instead of cameras 102 and 107 and that anyutilization device (such as a VCR) can be used instead of televisionsets 103 and 106. Also installed at cable subscriber locations 101 and105 are conventional voice telephone sets 109 and 119, respectively,which have standard local loop connections 113 and 118 to nodes withinrespective local exchange carrier (LEC) networks 140 and 145 (describedbelow) and between which conventional voice communication paths can beestablished through the IXC and/or LEC networks.

Switched digital network 160, as shown in FIG. 1, may include a singleswitch or a plurality of switches, including ISDN-capable switcheswithin POPs 161 and 162 as well as other switches shown as "nodes"163-165 in FIG. 1. The switches are interconnected by suitabletransmission and signaling facilities, including trunks 192 andincluding standard common channel signaling, or CCS, facilities 190,that are themselves well known and form no part of the presentinvention. Suffice it to say that the digital network is arranged toroute calls, which can be digitally encoded to represent audio and videoinformation, as well as associated routing and control signals, to theappropriate destination. For the purposes of controlling network callflow, carrier 150 includes a number of network control points (NCPs),such as NCPs 184 and 186 discussed in more detail below. The networkfurther includes so-called signal transfer points (STPs) 191 which areinterconnected with each other, with the NCPs, and with the variousswitching nodes via CCS signaling paths 190 shown as dashed lines.

Also shown in FIG. 1 are local exchange carrier (LEC) networks 140 and145, which include LEC nodes such as nodes 141 and 146. Nodes 141 and146 are ISDN-capable digital switches and have trunk connections 151 and152 to POPs 161 and 162, respectively. Additionally, signaling lines 142and 147 connect LEC nodes 141 and 146 to respective STPs 143 and 148.The latter, in turn, are connected to respective STPs 191 within network160 via signaling lines 144 and 149. Such signaling interconnectionsbetween the LECs and interexchange carriers such as AT&T are notcurrently ubiquitous, but are required in order to provide ISDNcapabilities such as 64 Kb/s transmission. Over time, it is expectedthat such signaling interconnections will, indeed, become ubiquitous orat least nearly so.

Also shown in FIG. 1 are originating ISDN subscriber location 110 anddestination ISDN subscriber location 115. These, again, areillustratively private residences although they need not be. Subscriberlocations 110 and 115 are connected to POPs 161 and 162 via other than acable television distribution network--specifically, via respectivetelephone facilities. In particular, subscriber locations 110 and 115are connected to LEC nodes 141 and 146, respectively, via ISDN BRI lines112 and 117. These locations illustratively are outfitted with ISDNvideo telephones 111 and 116 which communicate video signals using CCITTRecommendations H.221 and H.261. The latter define an internationalvideo compression standard for digitization and compression of videosignals at rates which are multiples of 64 Kb/s (i.e., 1×64 Kb/s upthrough 30×64 Kb/s). LEC nodes 141 and 146, in turn, respectivelyconnect subscriber locations 110 and 115 to POPs 161 and 162 as alreadynoted.

The overall combination of the IXC and LEC switchedfacilities--including those which provide both conventional andISDN-based switched voice, video and other switched communicationsservices--can be viewed as a single switched telecommunications network.

In accordance with the invention, the system of FIG. 1 is able to effectconnections between any pair of subscriber locations, be they cablesubscriber locations or ISDN subscriber locations. There are thus fourcases to consider, because either one of the originating and thedestination locations can be either a cable subscriber location or anISDN subscriber location.

We will now consider each of these possibilities in turn.

Looking, first, at the ISDN-to-ISDN case, it will be appreciated thatonly some of the equipment described hereinabove will, in fact, beinvolved. Specifically, originating ISDN subscriber location 110initiates a video telephone call to destination ISDN subscriber location115 by dialing the telephone number associated with the latter, i.e.,the telephone number assigned to BRI line 117. That telephone number maybe thought of as an "address" identifying the destination location.Since locations 110 and 115 are served by different LECs, the call isrouted from LEC node 141 to interexchange carrier 150 and, moreparticularly, to POP 161 within switched digital network 160. POP 161recognizes this as a video telephone call by virtue of unique signalingidentifying the call as a video telephone call, that signaling beingcontained, initially, within the D channel of BRI connection 112 and,thereafter, within CCS messages forwarded to POP 161 from LEC node 141.Upon recognizing this as a video telephone call, network 160 needs todetermine whether the destination location is an ISDN subscriberlocation or a cable subscriber location. To this end, POP 161 triggers aquery to video NCP 184, which includes a database which lists all of thevideo telephone cable subscriber locations. Specifically, a messagewhich includes the dialed telephone number is forwarded to NCP 184requesting a determination as to whether the destination location is oris not registered as a cable subscriber location. In this example, thedestination location is, in fact, an ISDN subscriber location and, as aresult, no database entry will be found. In this case, NCP 184--which,as noted above, knows the called telephone number--will instruct POP 161to route the call to LEC node 146. From this point forward, the callproceeds like any other ISDN call. Specifically, POP 161 routes the callthrough network 160 to POP 162 in conventional fashion. The latter, inturn, forwards the call to LEC node 146 which completes the call to ISDNsubscriber location 115.

Inasmuch as this turned out to be an ISDN-to-ISDN call, it will beappreciated that the call could have proceeded without an NCP lookup.That is, the call could, in theory, have been treated as a "standard"ISDN call which could have been routed, in the first instance, directlyto the destination ISDN location. However, since it is not known apriori whether a call coming in to POP 161 is being made to a cablesubscriber location or to an ISDN subscriber location, the lookup mustbe carried out in order to learn what type of equipment awaits at thedestination location.

The second case is the cable-to-cable case (e.g., cable subscriberlocation 101 originating a call to destination cable subscriber location105). In particular, the subscriber at originating cable subscriberlocation 101 initiates a call by pushing a START button, S, on NIU 104(or on a remote control device which sends signals to NIU 104) in orderto initiate a request signal that is equivalent to an off-hook messageused in conventional telephony, that request signal indicating a desireto originate a video telephone call. This off-hook message is sent toVESP 125 when NIU 104 is polled thereby (by way of cable head end 124).As explained in more detail in conjunction with FIG. 3, VESP 125includes a processor 360 (preferably a fault-tolerant mini-computer) andan associated database 361 which contains identity codes for the NIUsthat are attached to cable distribution network 121 and which also keepstrack of the upstream and downstream channel status on that network,administers scrambling codes, and performs other "housekeeping" tasksnot here relevant.

The NIU constantly receives a signaling message from the VESP indicatingthe status of the channels over the coaxial cable distribution network121 through a reserved portion of the bandwidth. Therefore, the NIUalways knows if there are free channels available or not. When thesubscriber initiates the call by pushing the START button, if there areno channels available, the NIU gives a busy signal to the subscriber.Otherwise, the NIU sends a message to the VESP to request a channelthrough a reserved portion of the bandwidth. If there were contention onthis signaling channel, the NIU must re-transmit. (This scheme issimilar to the well-known ALOHA system.) After reception of a clearmessage from the NIU by the VESP, the VESP transmits a message to theNIU directing it to communicate on a particular pair of channels. Afterthis time, all other signaling is done at the assigned channel. Then,the NIU is directed to transmit a signal representing the videotelephone number of the desired destination location which was suppliedby the subscriber via a dialing pad associated with the NIU along withinformation identifying the originating NIU to processor 360, whichpackages it into an ISDN-PRI signaling message that is sent to POP 161.

Pursuant to the invention described in the commonly assigned UnitedStates patent application of A. C. Papanicolaou and C. D. Yu entitled"Video Telephony Dialing," filed of even date herewith, the videotelephone number for a cable subscriber location--which, again, may bethought of as an "address" identifying same--is administered to be thesame as the standard ten-(i.e., area code plus seven-) digit localexchange carrier telephone number used for regular voice telephone callsdirected to that location. This may be seen from the enlarged view ofdestination cable subscriber location 105 in FIG. 10 showing that thelocal exchange carrier telephone number associated with local loop 118and standard telephone set 119 is the same as the video telephone numberassociated with NIU 108. In this case, then, the subscriber atoriginating cable subscriber location 101 would have entered on theNIU's keypad the ten-digit telephone number associated with telephoneset 119 installed at destination cable subscriber location 105, i.e.,the telephone number assigned to local loop connection 118. This isadvantageous in that, apart from the fact that acable-subscriber-originated video call, rather than a conventional voiceonly call, is being made, the subscriber at an originating cablelocation is given the illusion that he/she is initiating a dial-upconnection similar to any other dial-up connection that proceedsexclusively through the telephone network, such as a simple voice-onlycall. That is, since the video telephone call is initiated to the sametelephone number that would have been used if this were a conventionalvoice call made to the desired destination subscriber location, itappears to the originating subscriber that all he/she has done is "dialup" the desired destination subscriber from what appears to be nothingmore or less than a video-capable "extension" telephone within theoriginating location. Additionally, subscribers can "give out" a singletelephone number to friends and other potential callers, not having todifferentiate between "my voice number" and "my video number" but yetstill being able to receive both kinds of calls directed to that sametelephone number.

At POP 161, the signaling information associated with thecall--including, for example, the called video telephonenumber--obtained from VESP 125 is used to trigger a query to NCP 184 inthe manner described above. Since in this case the called location is,in fact, a cable subscriber location, NCP 184 accordingly instructs POP161 to route the call to VESP 129 via switched digital network 160.

The destination NIU 108 receives from cable head end 128 a) upstream anddownstream channel assignments and b) appropriate descrambling codes,and it activates a ringer to inform the called subscriber at thelocation of an incoming video telephone call. After the called partypushes a START button (equivalent to "off-hook" in telephony), theincoming audio/video signals are fed to television set 106 and camera107 sends its audio/video signals though the assigned upstream channelto the calling party's television.

After two-way communication has been established between locations 101and 105, either location can terminate the call by activating an ENDbutton, E, at NIU 104 or 108, or at a remote control device whichcommunicates with the NIUs. The END signal is transmitted in theupstream data communication channel to the attached head end (122 or127), and interpreted in a manner equivalent to an on-hook signal intelephony, namely to instruct switched digital network 160 to terminatethe video telephone call and tear down the connection therethrough.

The third case is the cable-to-ISDN case (e.g., cable subscriberlocation 101 originating a call to destination ISDN location 115). Sucha call proceeds identically to the cable-to-cable case up through thequery of NCP 184, this being a consequence of the fact that theequipment at the destination location (cable TV or ISDN) is not knownuntil the database lookup has been effectuated. ISDN subscriber location115 is not listed in database 184. Moreover, it may be assumed that anISDN video telephone at a residence is not one which is capable ofoperating at 384 Kb/s, which is the rate at which signals are generatedby VESP 125. Rather, 128 Kb/s is the most likely case. A video telephonesignal at that lower speed must thus be supplied to destination ISDNlocation 115.

Typically, however, the node within POP 161 will not be capable ofconverting the call to a call at a lower speed (although it is possibleto enhance the POP 161 and VESP 125 to provide this capability).Accordingly, NCP 184 will return a message to POP 161 instructing it toclear the call. The POP, in turn, will return a call-clearing message toVESP 125 in standard fashion.

The fact that the call was cleared at POP 161 will be taken by VESP 125as an indication that the destination location is neither a cablesubscriber nor a video telephone that can support a 384 Kb/s signal. Asa result, the VESP will a) assume that the terminal equipment can onlysupport a 128 Kb/s signal, b) will re-digitize the analog signalreceived from cable head end 124 at the lower rate, and c) willreinitiate a call to POP 161 at that rate. The messaging whichaccompanies the call request will be such as to inform POP 161 that nodatabase query is required but that, rather, the call should beimmediately routed over switched digital network 160 based on thedestination telephone number supplied, thereby re-establishing the callat the lower rate. From this point, the call proceeds just as in theISDN-to-ISDN case.

(As is well known, a 128 Kb/s connection is conventionally implementedby establishing two 64 Kb/s connections through the network, thoseconnections being synchronized by the endpoint terminals. Forconvenience of exposition herein, reference to a digital connection, orcall, should be understood to comprise such a pair of 64 Kb/s calls.)

The fourth case is the ISDN-to-cable case, e.g., ISDN subscriberlocation 110 originating a call to destination cable location 105. Inparticular, the call proceeds identically to the ISDN-to-ISDN case upthrough the query of NCP 184. Here, destination location 105 is, infact, listed in the database as a cable subscriber location. Therefore,NCP 184 will return instructions to POP 161 to route the call todestination head end 127 through POP 162. From this point on, the callis like a cable-to-cable call except that the transmission rate isdetermined by the rate at which the call was established which, in turn,depends on the capabilities of ISDN originating location 110. VESP 129is capable of handling calls at various rates and, in each case, ofconverting the received video telephone signals to the analog formrequired by destination cable subscriber location 105.

In the examples given above, it was tacitly assumed that the originatingand destination parties are provided with telephone service in differentso-called local access and transport areas, or LATAs. If they were inthe same LATA, a call from ISDN location 110 to ISDN location 115 wouldhave been handled without being routed through an interexchange carrier.Since both of those locations are ISDN locations, this is no problem.The call will be treated by the LEC as a standard intra-LATA ISDN call.A different situation arises, however, if the destination location is acable subscriber but is still within the same LATA as the originatingsubscriber. In this case, the LEC will, in the first instance, interpretthe call request as being a request to complete a call to an ISDNsubscriber. Since the called subscriber does not have ISDN service, thiscall will simply fail at the destination LEC node.

One way to resolve this issue is for the LECs to provide connections tothe VESPs, thereby in effect replicating, for local calls, thefunctionality of interexchange carrier 150, as described above.Assuming, however, that the LECs do not offer this capability, analternative way of providing service in this case is to provide the ISDNsubscriber locations with a mechanism for accessing interexchangecarrier 150 directly. One such mechanism is to provide the ISDNsubscriber with a telephone number which can be dialed to initiate anISDN-to-cable connection.

More particularly, the call--which is assumed in this example to be an800-type call--would begin from originating ISDN location 110 as a voicecall, inasmuch as digital 800 service is not currently offered byinterexchange carriers. By virtue of the number dialed, the call will berouted by LEC network 140 to POP 161 via trunk 151. POP 161, in turn,will request instructions for handling this call from 800 NCP 186. Thelatter determines from its associated 800 number database that this is,in fact, a video telephone call and instructs POP 161 to route the calltemporarily to voice response unit 166 which may be, for example, aConversant® voice response unit available from AT&T. Voice response unit166 presents audio announcements to the originating subscriberrequesting the telephone number of the destination location and, uponreceiving same via touchpad input from the subscriber, establishes a newcall to destination head end 127, through POP 161, by using thedestination address provided by the subscriber. By virtue of the factthat this call is destined for VESP 129 rather than LEC node 146, POP161 initiates a lookup to NCP 184 which in turn provides correct routinginstructions to POP 161 for routing the call to head end 127. If anentry for the latter cannot be found in NCP 184, the caller is alertedby the voice response unit 166 that the call cannot be completed. Eitherthe call is terminated at this point or the originating subscriber isgiven another opportunity to supply a valid destination telephonenumber.

Assuming, however, that an entry for the destinationlocation--illustratively, location 105--is found in NCP 184, then NCP184 returns to POP 161 instructions to route the call to VESP 129through POP 162. At this point, voice response unit 166 bridges the callreceived from the calling subscriber to the call itself initiatedtowards the called subscriber. This in effect gives the the callingsubscriber of the second call as a progression of the first call. Sincethe current capabilities for 800-type calls are such that only voicecalls can be supported, the call received by VESP 129 at this time isnot a digital video telephone call, as was the case in the examplesgiven above, but, rather, is a voice call. In order to establish adigital connection which can support video telephony, it is necessaryfor VESP 129 to initiate the setting up of a digital connection betweenitself and originating ISDN location 110. To this end, VESP 129 maydeliver an audio message to originating ISDN location 110 instructingthe originating subscriber to hang up and wait for a return digitalcall. VESP 129 first checks to ensure that the destination customer orthe access channels to that customer are not busy. Provided that this isthe case, VESP 129 thereupon uses the number which was supplied by POP162 with the voice call to set up the call. With the call between theoriginating ISDN location 110 and destination head end 127 thusestablished, the latter can proceed to establish a link from itself tothe destination cable subscriber location 105 in the same way that itwould for any other incoming video telephone call. If, on the otherhand, the destination customer is found to be busy, an appropriateannouncement, e.g., busy tone, is provided to the calling subscriber.

The foregoing is merely illustrative and various enhancements arepossible. For example, it was assumed hereinabove that an ISDNsubscriber location will not be registered in NCP 184 and will have aspecific type of video telephone, e.g., a video telephone whichcommunicates at 128 Kb/s. It is possible, however, to maintain in thatsame database subscription information about ISDN subscriber locations,as well. Such information may include the data rate at which thesubscriber's equipment operates so that different ISDN video telephonescan be supported in a graceful way. The retrieval of such data by NCP184 would result in explicit instructions being sent to VESP 125 throughPOP 161. The VESP, in turn, can use this information to initiate thesetting up of a call at the appropriate rate for the destination ISDNsubscriber location.

As a further enhancement, a cable subscriber location may also have anISDN line so that the subscriber can a) use his/her ISDN (videotelephone) if the other location also comprises an ISDN video telephone,or b) use his/her cable-connected equipment if the other location hasthat type of equipment. This can be easily accomplished bycross-referencing the incoming call type with the subscription datastored in NCP 184 and routing calls accordingly.

Another possible enhancement is the incorporation of the concept of a"learning database." When data on a given called customer is not foundin video NCP 184, calls at likely data rates can be made to see, bytrial and error, which data rate indeed is appropriate for the calledsubscriber. This information can thereafter be stored in video NCP 184so that subsequent calls to the subscriber can proceed automatically.

The logical sequence of steps implemented within network 160 to achievethe above-described various forms of connections is summarized by theflowchart of FIG. 8, beginning when POP 161 receives a call request atstep 801. If the call was not originated from a cable head end, as isdetermined at step 820, it is assumed to be an ISDN call. It is thendetermined from the D channel at step 810 whether this is a video call,as opposed to any other type of ISDN call. If it is the latter, the ISDNcall is simply completed in the conventional way, as indicated at step824. If, on the other hand, this is a video call, then NCP 184 isqueried at step 812 to determine, as tested at step 814, whether thedestination location is a cable subscriber location. If it is, the callis routed to the destination head end, as indicated at step 822, thisbeing the ISDN-to-cable case. If, on the other hand, the destinationlocation is a not a cable subscriber location (or, as mentioned above asa possibility, it is a subscriber location that has both cable and ISDNcapabilities) the call can, again, be completed as a normal ISDN call,this being the ISDN-to-ISDN case.

Returning to step 820 and assuming, now, that the call was originatedfrom a cable head end, a test is first made at step 830 as to whetherthis is a "no query," meaning that the originating head end indicates incall setup request that no query is needed for routing this call. Ifthis is a "no query" call, the call is completed as an ISDN call at step824. As noted earlier, the bit rate for the "no query" call is eitherthe default rate of 128 Kb/s or some other appropriate rate, if theoriginating head end has been given explicit bit rate information aboutthe destination location from NCP 184 when the call was cleared. If thisis not a "no query" call, NCP 832 is queried at step 832 and the natureof the destination location is tested at step 834. If the destinationlocation is a cable subscriber location (or, as mentioned above as apossibility, it is a subscriber location that has both cable and ISDNcapabilities), the call is routed to the destination head end asindicated at step 822. This is the cable-to-cable case. If thedestination location is not a cable subscriber location, it is presumedto be an ISDN location. Indeed, NCP 184 may contain informationindicating that the destination location is capable of receiving 384Kb/s video, in which case the signal from the originating head end,which is also a 384 Kb/s signal, can be immediately forwarded to thedestination location as an ISDN call from that point, per steps 836 and824. If NCP 184 does not indicate that the destination location iscapable of receiving 384 Kb/s video--either because it has informationindicating that the destination location operates at a lower speed orbecause it has no information about that location at all--the call iscleared back to the originating head end, as indicated at step 826, thecall clearing message including the destination rate information if itis available.

FIG. 9 shows a small portion of the subscriber database maintainedwithin video NCP 184. Three information fields of particular relevanceto the invention--"subscriber video telephone number," "cable subscriberrouting information," and "ISDN subscriber rate information"--arerepresented explicitly in the FIG., with other fields simply beingdenoted as such. These data elements can be entered through a"subscription-time" questionnaire or through the actions of a learningdatabase, as alluded to earlier.

Three illustrative data records within the database are shown. Record901 is a record for a subscriber location which is only a cablesubscriber location. Indeed, it is the record for cable subscriberlocation 105. This record thus contains the subscriber video telephonenumber and cable subscriber routing information, but no ISDN subscriberrate information. The cable subscriber video telephone number is (203)555-6721. As noted earlier and as shown in FIG. 10, this video telephonenumber is illustratively the same as the local exchange carriertelephone number associated with local loop 118 to which is attachedstandard telephone set 119 within the subscriber location. The cablesubscriber routing information--retrieved when video NCP 184 is accessedusing the subscriber video telephone number supplied thereto--is used toroute video calls to the subscriber location including, for example, anidentification of the destination POP, destination head end, and a codeuniquely distinguishing the destination location from all others servedby that head end, thereby establishing an association between thetelephone number and the cable television distribution networkassociated with the destination cable subscriber location. In record901, this routing information is symbolically represented as162/127/126/108, which are the reference numerals for the variouselements of the route to NIU 108 within subscriber location 105.

Record 902 is a record for a subscriber location which is only an ISDNlocation--illustratively ISDN subscriber location 110. As such, therecord contains a) a subscriber video telephone number which, in thiscase, identifies ISDN connection 112, and b) information about the rateat which the ISDN video telephone 111 installed at that locationoperates--symbolically represented in FIG. 9 by a "384", meaning 384Kb/s. (It will, of course, be remembered that an ISDN destinationlocation need not have an associated record in the NCP in order for itto receive calls. In the absence of such a record, a default rate of 128Kb/s is assumed.)

Record 903 is a record for a subscriber location which is both a cablelocation and an ISDN location--illustratively one of the locations (notshown) connected to distribution network 121. Here all three of thefields have entries, including an entry indicating that the ISDN videotelephone at that location operates at a rate of 128 Kb/s. (It will berecalled that, for such locations, calls would typically be directed tothe cable (ISDN) equipment if the originating equipment is cable (ISDN)equipment.)

The remainder of this detailed description and the associated portionsof the drawing describe and show details of the various components ofthe system of FIG. 1.

Referring, in particular, now to FIG. 2, there is illustrated in blockdiagram form an analog network interface unit (such as NIU 104 or 108 inFIG. 1). This NIU is used in embodiments in which digital coding anddecoding is not available in originating and destination locations. Inthis embodiment, audio and video signals generated in an originatinglocation are provided to the NIU on individual inputs 211 and 212,respectively, while audio and video signals are output from the NIU onindividual outputs 221 and 222, respectively. The NIU is connected to acable distribution network through a coaxial cable 250, for the purposeof sending and receiving frequency modulated signals, typically in the5-550 MHz frequency band, via a diplex filter 240. The functions offilter 240 are: (1) to provide a high-frequency band pass (e.g., 50 to550 MHz) between coaxial cable 250 and the downstream data channeldemodulator 227 as well as the downstream video telephone channel to IFdemodulator 225; (2) to provide a low-frequency band pass betweencoaxial cable 250 and the upstream data channel modulator 217 as well asthe IF to upstream video telephone channel modulator 215. Thiscapability exists in most two-way coaxial cable amplifiers. Within theNIU, a microprocessor 270 receives information from dialing pad 272 andfrom downstream data channel demodulator 227, which demodulates thedownstream data communication carrier frequency to retrieve controlinformation sent from a VESP. The downstream control information mayinclude the following messages: (1) polling message; (2) upstream videotelephone channel assignment message; (3) downstream video telephonechannel assignment message; (4) descrambling authorization message; (5)Caller ID; and possibly other auxiliary information.

Video telephone signals generated in the originating location anddestined for the destination location are processed in the NIU bymodulating a carrier to form an RF signal illustratively having anapproximate 6 MHz bandwidth. This is done so that several(illustratively four) upstream video telephone "channels" will exist oncoaxial cable 250. Of course, other arrangements may utilize fewer oradditional channels or channels of less than 6 MHz bandwidth. Modulationis accomplished in two stages, first to an intermediate (IF) frequencyin baseband to IF modulator 213, and then to the desired channelfrequency in IF to upstream video telephone channel modulator 215. Theparticular channel center frequency selected and used in modulator 215is under the control of a microprocessor 270, through its interpretationof the upstream video telephone channel assignment message.

Incoming video telephone signals are processed in the NIU of FIG. 2 bytuning (frequency demodulating) the RF signal received on coaxial cable250 to recover the embedded audio and video information. Demodulation isaccomplished in two stages, first by a downstream video telephonechannel to IF demodulator 225 and then by an intermediate frequency tobaseband demodulator 223. The particular channel center frequency usedin demodulator 225 is selected under the control of microprocessor 270through its interpretation of the downstream video telephone channelassignment message received from the associated head end. In order toassure that only the desired party can receive and utilize the incomingaudio/video information, the downstream signal is scrambled (inscramblers 371-373 in the destination side VESP, as explained more fullyin FIG. 4). Descrambler 230 is arranged to descramble the scrambled IFsignal output from demodulator 225, under the control of microprocessor270 through its interpretation of the descrambling authorization messagereceived from the associated head end.

Microprocessor 270 also receives inputs from the user of the NIU of FIG.2, illustratively via keypad 272, in order to obtain information abouteach video telephone call, such as on-hook and off-hook status, dialednumber, billing information, authorization number, and so on. Thisinformation is applied to a separate upstream data channel modulator217, illustratively an FSK modulator, which converts the digital data toa modulated signal that is also transmitted via coaxial cable 250.

Before describing the remaining portions of the system, it will beinstructive to describe here the arrangement of a digital NIU used inembodiments in which digital encoding and/or decoding is available ineither an originating location, a destination location, or both. Such adigital NIU is illustrated in block diagram form in FIG. 6. In thisfigure, as in FIG. 2, analog audio and video signals generated in anoriginating location are provided to the NIU on individual inputs 211and 212, respectively, while analog audio and video signals are outputfrom the NIU on individual outputs 221 and 222, respectively. As in FIG.2, the digital NIU of FIG. 6 is connected to a cable distributionnetwork through a coaxial cable 250, for the purpose of sending andreceiving frequency modulated signals, typically in the 5-550 MHzfrequency band, via diplex filter 240.

The NIU of FIG. 6, like its counterpart in FIG. 2, includes amicroprocessor 270 which receives information from dialing pad 272 andfrom downstream data channel demodulator 227 and which demodulates thedownstream data communication carrier frequency to retrieve controlinformation sent from the VESP. The analog audio/video signals comingfrom inputs 211 and 212 are first digitally encoded in video coder 253to form a digital bit stream, which is then modulated in an upstreamvideo telephone channel modulator 255 onto an assigned digital upstreamvideo telephone channel using a carrier frequency that is associatedonly with that channel. The particular channel center frequency selectedand used in modulator 255 is under the control of microprocessor 270,through its interpretation of the upstream video telephone channelassignment message received from the associated head end. Note thattwo-step modulation (baseband to IF, and IF to channel frequency) is notrequired in this embodiment.

With respect to downstream signals, incoming digitally encoded videotelephone signals are retrieved in the digital NIU of FIG. 6 bydemodulating the specific downstream digital video telephone channel indownstream video telephone channel demodulator 265. The particularchannel center frequency used in demodulator 265 is selected under thecontrol of microprocessor 270 through its interpretation of thedownstream digital video telephone channel assignment message receivedfrom the associated head end. In order to assure that only the desiredparty can receive and utilize the incoming digital audio/videoinformation, the downstream signal is scrambled (in digital scrambler371 in the destination side VESP, as explained more fully in FIG. 4).Digital descrambler 250 is arranged to descramble the scrambled digitalsignal output from demodulator 265, under the control of microprocessor270 through its interpretation of the descrambling authorization messagereceived from the associated head end. The output of descrambler 250 isapplied to video decoder 263 which converts the digital signal toaudio/video signals in the appropriate format (e.g., NTSC format) forapplication to the terminating devices, e.g., a television set ormonitor. Note that two-step demodulation (i.e., from video telephonechannel to IF and from IF to baseband) is not required in thisembodiment.

FIG. 3 illustrates, in block diagram form, a typical arrangement forcable head ends, such as head ends 124 and 128 of FIG. 1. The functionof a cable head end is, in general, to act as signal converter andchannel combiner and splitter for the coaxial bandwidth of a cabledistribution network.

More specifically, as shown in FIG. 3, a cable head end 300 is arrangedto receive RF signals from coaxial cable 302 via a diplex filter 340similar to filter 240 of FIG. 2, or FIG. 6, which acts like a hybrid andseparates incoming and outgoing signal streams, and separates videotelephone channel signal streams from entertainment channel signalstreams. Signals in the upstream video telephone bandwidth, e.g., 5-30MHz, are applied to upstream channel splitter 305, which filters andseparates the incoming signals on the basis of carrier frequency, andapplies the individually modulated RF signals to a plurality ofdemodulators 307-309, each having the appropriate carrier frequency.

Downstream video telephone signals output from downstream videotelephone channel modulators 327-329 in the digital portion of the headend are combined with other entertainment channels, constituting adownstream bandwidth, e.g., 50-550 MHz, in downstream channel combiner335.

FIG. 4 illustrates in block diagram form a typical arrangement for aVESP, such as VESPs 125 and 129 of FIG. 1, which serve as an interfacebetween the cable distribution network and a digital transmissionfacility such as a T1 or T3 transmission facility operating with theISDN PRI protocol. In the VESP, upstream analog video telephone channels(two channels being illustrated in FIG. 4) terminate on upstream analogvideo telephone channel to IF demodulators 308 and 309, while anupstream digital video telephone channel (one channel being illustratedin FIG. 4) terminates on upstream digital video telephone channeldemodulator 307.

The output from each upstream video telephone channel demodulator307-309 feeds into a respective 1×2 switch 391-393. There are twooutputs of each of those 1×2 switches. One goes to an input port of anN×M switch 395, where N is the number of incoming analog video telephonechannels and M is the number of outgoing video telephone channels. Thesecond output from switches 391 and 392 goes to the IF to basebanddemodulator 382 and 383, while the second output from switch 393 goesdirectly to multiplexer/demultiplexer (MUX/DUX) 330. This differenttreatment results from the fact that the output of demodulator 307 isdigital, and thus does not require IF to baseband demodulation anddigital coding, as do the outputs from demodulators 308 and 309, whichare analog.

Both 1×2 switches 391-393 and N×M switch 395 receive controlinstructions from processor 360 which distinguish inter-cable videotelephone calls and intra-cable video telephone calls. If, for example,the upstream analog video telephone signal demodulated by demodulator309 is to be transported to a remote location in another cabledistribution system, 1×2 switch 391 will connect its input to IF tobaseband demodulator 383. If, in the other case, the upstream analogvideo telephone signal demodulated by demodulator 309 is to betransmitted to a destination location in the same cable distributionsystem (intra-cable video telephone call) via one of the analogdownstream video telephone channels, 1×2 switch 391 will connect itsinput to N×M switch 395. The function of the N×M switch is to connectsuch an upstream analog video telephone signal directly to one of thedownstream analog video telephone channels. For this purpose, theoutputs of N×M switch 395 are connected to IF to downstream videotelephone channel modulators 328 and 329, via scramblers 372 and 373,which are used so that only the intended destination location canrecover and use the transmitted audio/video signals.

With respect to digital (as opposed to analog) signals received in theVESP of FIG. 4, processing of the upstream digital video telephonesignal demodulated by demodulator 307 also depends on whether thedestination location is connected to the same cable distribution networkas the originating location (i.e., an intra-cable system call) or to adifferent cable distribution network (i.e., an inter-cable system call).If the call is destined for a destination location in another cabledistribution system, 1×2 switch 393 connects its input to MUX/DUX 330.If, in the other case, the upstream digital video telephone signaldemodulated by demodulator 307 is to be transmitted to a destinationlocation in the same cable distribution system via one of the downstreamdigital video telephone channels, 1×2 switch 393 connects its input toN×M switch 395. As before, the function of N×M switch 395 is to connectthe upstream digital video telephone signal to one of the downstreamdigital video telephone channels. For security purposes, the downstreamdigital video telephone signal is scrambled in digital scrambler 371before being applied to downstream digital video telephone channelmodulator 327.

The baseband audio and video signals output from IF to basebanddemodulators 382, 383 are essentially similar to the original analogaudio and video signals generated in the originating location. However,due to the fact that incoming audio played from the TV set may be pickedup by the microphone of the camcorder, echo cancelers 312, 313 may bearranged to eliminate echo in the audio signals, in a manner well knownto those skilled in the art. In order to convert the audio and videosignals to digital form, the video outputs of demodulators 382, 383 andthe audio outputs from echo cancelers 312, 313 are applied to aplurality of codecs 322, 323, which illustratively provide a digitaloutput at 384 Kb/s. Many codecs of this kind are commercially availablesuch as those that are marketed by Compression Labs, Model RembrandtII/VP. The outputs of codecs 322, 323 and the digital video telephonesignals from the upstream digital video telephone channels are combinedin a time division multiplexer 330 having ISDN PRI protocol capability.The output of MUX/DUX 330 is applied via digital transmission facility(ISDN PRI) 350 to switched digital network 160.

In the reverse direction, multiplexed composite signals from digitalnetwork 160 are received in the VESP of FIG. 4 via digital transmissionfacility 350. Individual digital signals destined for differentdestination locations are recovered by demultiplexing in MUX/DUX 330,which performs the demultiplexing function in a manner complementary tothe multiplexing function performed on upstream signals, according tothe video telephone channel assignment messages generated in the VESPs.The demultiplexed bit streams from MUX/DUX 330 are applied to codecs322, 323 or directly to digital scrambler 371 if the bit streams aredestined for locations with video decoding equipment.

The digital signals applied to codecs 322, 323 are first decompressedand then converted back into individual baseband audio and videosignals. These baseband outputs are modulated to IF in baseband to IFmodulators 332, 333 and then scrambled in scramblers 372, 373, and thescrambled IF signal is then frequency modulated in modulators 328, 329.As stated previously, modulators 328, 329 have different carrierfrequencies corresponding to the downstream analog channels on the cabledistribution network that are allocated for video telephone calls. Theoutputs of modulators 327, 329 in the downstream bandwidth (e.g., 50-500MHz) are combined with the entertainment channels in downstream channelcombiner 335 in cable head end 300 and applied to cable 302.

If a demultiplexed digital (rather than analog) signal is destined for alocation equipped with video decoding equipment, such a signal need notbe converted back to analog form via a codec in the head end. Rather,such a signal is first scrambled by digital scrambler 371 and thenmodulated to an assigned downstream digital video telephone channel viadownstream digital video telephone channel modulator 327.

Because video telephone signals in all downstream channels are appliedto all NIUs connected to the cable distribution network 302, the analogscrambling provided in scramblers 372, 373 and the digital scramblingprovided in scrambler 371 is necessary for privacy reasons. This assuresthat the audio/video information can only be used by the particular userfor which it is destined because only that user can descramble thesignal. For this purpose, only an addressed NIU will receive thedescrambling code. An analog NIU will activate its respective analogdescrambler 230 and a digital NIU will activate its respective digitaldescrambler 250 in order to reassemble the received analog or digitalaudio/video information.

Part of the upstream bandwidth that is split out of the signal receivedby splitter 305 in the cable head end is a control signal in an upstreamdata communication channel which is demodulated in an upstream datacommunication channel demodulator 346 in the VESP. The retrievedupstream control signal is fed into processor 360, and then combined inMUX/DUX 330 with digitized video telephone signals before beingtransmitted to digital network 160 via transmission facility 350. Thefunctions of processor 360 are (1) to perform polling; (2) to controlthe N×M switch 395, and the 1×2 switches 391-393; and (3) to control themultiplexer/demultiplexer 330. Local database 361, which operates withprocessor 360, contains the address and type of all of the NIUsconnected by the cable network, and the video telephone channel status.This information is used for polling the NIUs. Downstream data messagesfrom digital network 160 are demultiplexed in multiplexer/demultiplexer330, and fed into processor 360. These messages, which are used tocontrol subscriber NIUs, are modulated in the downstream datacommunications channel by modulator 316, and combined with otherdownstream video telephone channels in downstream channel combiner 335.

Filter 340, together with splitter 305 and combiner 335, operate onanalog signals. The distance between the splitter 305 (or combiner 335)and demodulators 307-309 (or modulators 327-329), which are part of theVESP 301, may vary from a few feet to many miles. In the former case,coaxial cables can be used for the connections while, in the lattercase, existing off-the-shelf analog fiber optic or microwavetransmitters and receivers can be used. While FIGS. 3 and 4 illustratetwo analog video telephone channels and one digital video telephonechannel, it is to be understood that fewer or more video telephonechannels may exist on cable 302, and accordingly, a different number ofdemodulators and modulators may be employed.

Referring now to FIG. 5, there is shown a block diagram illustrating thearrangement of point of presence (POP) equipment 401 which isillustratively used to realize POPs 161 and 162 of FIG. 1 in moredetail. POP 401 includes a multiplexer/demultiplexer 441 and aninter-connected digital switch 442 such as an AT&T 4ESS digital switch.Upstream signals, typically in the PRI Q931 protocol, are received inthe POP from a VESP and applied to multiplexer/demultiplexer 441. Thesesignals, which include several--illustratively three in FIG. 5--videotelephone information signals as well as signaling information, aredemultiplexed in multiplexer/demultiplexer 441 to separate signalinginformation from user data. The user data outputs are applied toindividual ports of switch 442 for routing to the appropriatedestination within digital network 160. Upstream control signals appliedto multiplexer/demultiplexer 441 are separately recovered on line 454 bythe switch.

If POP 401 in FIG. 5 is the destination for video telephone informationsignals, switch 442 receives signaling information indicating, forexample, the ultimate destination for the call. The incoming videotelephone information signal received in switch 442 is coupled to line471, which also connects switch 442 to multiplexer/demultiplexer 441,while the control messages are also passed on a separate line 474. Inmultiplexer/demultiplexer 441, the individual video telephoneinformation signals from various sources are combined with each otherand with control messages relating thereto, and transmitted to the VESP,again typically using PRI Q931 protocol.

The foregoing merely illustrates the invention. Those skilled in the artwill be able to devise numerous arrangements which, although notexplicitly shown or described herein, embody the principles of theinvention and are within their spirit and scope.

We claim:
 1. A system for establishing a video telephone call, saidsystem comprisingoriginating means for communicating a video telephonesignal from an originating video telephone location to a first point ofpresence, a switched digital telephone network for routing said signalfrom said first point of presence to a second point of presence, anddestination means for communicating said video telephone signal fromsaid second point of presence to a destination video telephone location,one of said originating and destination means comprising a cabletelevision distribution network and the other of said originating anddestination means comprising a facility other than a cable televisiondistribution network.
 2. The invention of claim 1 wherein said other ofsaid originating and destination means comprises a telephone facility.3. The invention of claim 1 wherein said originating means is arrangedto initiate said call at a first data rate and to re-establish said callat a second, lower data rate in response to a signal received from saidnetwork indicating that said destination means is other than a cabletelevision distribution network.
 4. The invention of claim 3 whereinsaid first data rate is 384 Kb/s.
 5. The invention of claim 4 whereinsaid second rate is 128 Kb/s.
 6. The invention of claim 1 wherein saidoriginating means comprises an ISDN connection between said originatingvideo telephone location and said first point of presence, and whereinsaid video telephone call is an ISDN video telephone call which includesinformation identifying said call as a video telephone call. 7.Apparatus for use in a telephone network, said apparatus comprisingmeansfor receiving video telephone signals from a plurality of originatingvideo telephone locations, and means for routing a video telephonesignal received from a particular one of said originating videotelephone locations to any selected one of a plurality of destinationvideo telephone locations, ones of said originating and destinationvideo telephone locations being cable subscriber locations connected torespective points of presence within said telephone network viarespective associated cable television distribution network connectionsand others of said video telephone locations being non-cable subscriberlocations connected to respective points of presence within saidtelephone network via respective associated telephone facilities that donot include cable television distribution network connections.
 8. Theinvention of claim 7 wherein said telephone facilities each include alocal loop connecting a respective one of said non-cable subscriberlocations to its respective point of presence via at least a first localexchange carrier node and a communications path connecting said node tothat point of presence.
 9. The invention of claim 7 wherein others ofsaid destination video telephone locations are both cable subscriberlocations and non-cable subscriber locations and wherein said routingmeans routes video telephone signals to an individual one of thoselocations via the latter's associated cable television distributionnetwork connection if the originating video telephone location is acable subscriber location and via its associated telephone facility ifthe originating video telephone location is a non-cable subscriberlocation.
 10. The invention of claim 7 wherein said telephone networkincludes means for recognizing an individual ISDN call made to saidnetwork as being a video telephone call destined for a selected videotelephone destination location, for determining if the selected locationis a cable subscriber location, for routing each such ISDN call to thecable television distribution network associated with the selectedlocation if that location was determined to be a cable subscriberlocation and for routing it as an ISDN-to-ISDN call otherwise.
 11. Theinvention of claim 7 wherein said telephone network includes means forrecognizing an individual ISDN call made to said network as being avideo telephone call destined for a selected video telephone destinationlocation identified by respective telephone number provided with thecall, wherein said network includes a database associating telephonenumbers with respective cable television distribution networks, andwherein said network is arranged to route said received ISDN videotelephone call to the cable television distribution network associatedwith said telephone number if such a network is identified in saiddatabase and, if such a network is not identified in said database, asan ISDN-to-ISDN call based on said telephone number.
 12. The inventionof claim 7 wherein said routing means includeslookup means responsive toan address signal identifying the selected destination video telephonelocation for determining if that location is one of said cablesubscriber locations, and means for routing the received video telephonesignal to a) the cable distribution network associated with the selectedvideo telephone location if that location is determined to be a cablesubscriber location and, otherwise, b) to a telephone line extending tosaid destination video telephone location and identified by said addresssignal.
 13. The invention of claim 12 wherein said address informationis the local exchange carrier telephone number associated with saidtelephone line.
 14. The invention of claim 12 wherein said lookup meansincludes database means which stores information about each of saidcable subscriber locations, said information including an identificationof the cable distribution network associated with said each cablesubscriber location.
 15. The invention of claim 14 wherein videotelephone signals are initially provided from said originating cablesubscriber locations at a first data rate, wherein said database meansfurther stores information about the data rate at which video telephoneequipments at ones of said non-cable subscriber locations operate, andwherein said network is arranged such that if said selected destinationlocation is determined to be a non-cable subscriber location and if adata rate associated with that location is stored by database means,said network signals the originating cable subscriber location toprovide its video telephone signal at that stored data rate.
 16. Theinvention of claim 12 wherein video telephone signals are initiallyprovided from originating cable subscriber locations at a first datarate and wherein said network is arranged to signal said particularoriginating cable subscriber location to provide its video telephonesignal at a second, lower rate if said selected video telephone locationis determined to be a non-cable subscriber location.
 17. The inventionof claim 16 wherein said lookup means includes database means whichstores information about ones of said non-cable subscriber locations andwherein said second rate is determined as a function of saidinformation.
 18. The invention of claim 16 wherein said first data rateis 384 Kb/s.
 19. The invention of claim 18 wherein said second rate is128 Kb/s.
 20. A method for use in a telephone network, said methodcomprising the step ofrouting a video telephone signal received from aparticular one of a plurality of originating video telephone locationsto any selected one of a plurality of destination video telephonelocations, ones of said originating and destination video telephonelocations being cable subscriber locations connected to respectivepoints of presence within said telephone network via respectiveassociated cable television distribution network connections and othersof said video telephone locations being non-cable subscriber locationsconnected to respective points of presence within said telephone networkvia respective associated telephone facilities that do not include cabletelevision distribution network connections.
 21. The invention of claim20 wherein said telephone facilities each include a local loopconnecting a respective one of said non-cable subscriber locations toits respective point of presence via at least a first local exchangecarrier node and a communications path connecting said node to thatpoint of presence.
 22. The invention of claim 20 wherein others of saiddestination video telephone locations are both cable subscriberlocations and non-cable subscriber locations and wherein said routingstep includes the steps ofrouting video telephone signals to anindividual one of those locations via the latter's associated cabletelevision distribution network connection if the originating videotelephone location is a cable subscriber location, and routing videotelephone signals to an individual one of those locations via thelatter's associated telephone facility if the originating videotelephone location is a non-cable subscriber location.
 23. The inventionof claim 20 wherein said telephone network includes means forrecognizing an individual ISDN call made to said network as being avideo telephone call destined for a selected video telephone destinationlocation, and wherein said routing step includes the steps ofdeterminingif the selected location is a cable subscriber location, routing eachsuch ISDN call to the cable television distribution network associatedwith the selected location if that location was determined to be a cablesubscriber location, and routing each such ISDN call as an ISDN-to-ISDNcall otherwise.
 24. The invention of claim 20 wherein said telephonenetwork includes means for recognizing an individual ISDN call made tosaid network as being a video telephone call destined for a selectedvideo telephone destination location identified by respective telephonenumber provided with the call, wherein said network includes a databaseassociating telephone numbers with respective cable televisiondistribution networks, and wherein said routing step includes the stepsofrouting said received ISDN video telephone call to the cabletelevision distribution network associated with said telephone number ifsuch a network is identified in said database and, routing said receivedISDN video telephone call as an ISDN-to-ISDN call based on saidtelephone number if such a network is not identified in said database.25. The invention of claim 20 wherein said network includes lookup meansresponsive to an address signal identifying the selected destinationvideo telephone location for determining if that location is one of saidcable subscriber locations, and wherein said routing step includes thestep ofrouting the received video telephone signal to a) the cabledistribution network associated with the selected video telephonelocation if that location is determined to be a cable subscriberlocation and, otherwise, b) to a telephone line extending to saiddestination video telephone location and identified by said addresssignal.
 26. The invention of claim 25 wherein said address informationis the local exchange carrier telephone number associated with saidtelephone line.
 27. The invention of claim 25 wherein video telephonesignals are initially provided from originating cable subscriberlocations at a first data rate and wherein said routing step includesthe further step ofsignaling said particular originating cablesubscriber location to provide its video telephone signal at a second,lower rate if said selected video telephone location is determined to bea non-cable subscriber location.